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Science Objectives
Previous satellites have mapped vegetation area in great detail, but VCL will be the first to map the vertical dimension of a forest. Where the leafs and twigs and branches are within a forest— how much is high in the canopy or near the ground in foliage—changes as a forest ages. These maps will provide a direct way to identify degraded areas, areas of regrowth, and intact forests. Biodiversity studies can use VCL's comprehensive assessment of forest structure and organization to identify and monitor important habitat areas. VCL will yield a 5-10 times improvement in estimates of forest canopy height, a measurement used to estimate total biomass. Biomass in forests represents the major reservoir of carbon in terrestrial ecosystems that can be quickly released by disturbance (such as wildfire) or land use change. Climate and weather forecasting models use approximations of surface cover in their calculations because the movement of the atmosphere and weather systems are influenced to some degree by the "texture" of land cover. Current estimates of surface cover, however, are based on very little data. VCL's direct measurements of canopy height and density over much of the world will be used in these models to represent more accurately the aerodynamic properties of the Earth's surface. Mission Overview
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 Vegetation Canopy
Lidar Top Left: The Vegetation Canopy Lidar (VCL) satellite. Due to launch in
the fall of 2000, VCL will provide information about the age, density, and complexity of
forests around the world. (Image by Eric F. Pfleckl, Orbital Sciences Corporation)
Bottom Left: The Laser Vegetation Imaging Sensor (LVIS), flown aboard an aircraft,
helped test the technologies to be used in VCL. (Image courtesy NASA GSFC Scientific Visualization Studio) | ||
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A New Application of Lidar Technology
Lidars send a short pulse of light energy from a laser at a target. The time it takes for each pulse to complete a roundtrip to and from the target is converted into a direct measure of the elevation of the target. VCL's Multi-Beam Laser Altimeter goes one step further by also recording the "waveform" of the returned signal. The unique shape of the waveform reveals where—in the space between the ground and the tree tops—the foliage, trunk, and branches are concentrated. VCL is the first multi-beam, waveform-recording lidar to fly in space.
The VCL lidar holds five lasers that each send 242 pulses per second at the Earth's surface. Each beam covers an area 75 feet across. By spacing the five beams a little over a mile apart, each VCL orbit will sample an area 5 miles across. The VCL science team is using the airborne Laser Vegetation Imaging Sensor (LVIS), built at NASA's Goddard Space Flight Center in Greenbelt, Md, to acquire VCL-like data that they will use to fine-tune their data analysis methods. LVIS uses one laser, but it maps 100 percent of an area more than a half mile wide at a single pass. A rotating mirror reflects each laser pulse out from the aircraft at a slightly different angle to hit a series of consecutive areas in a strip across the flight path. next: Applications to Forest Management Needs
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 Vegetation Canopy Lidar |
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Application to Forest Management Needs
Most of the information available to forest managers on the structure of forests is very spotty, requiring labor-intensive sampling from the ground. For the USDA Forest Service in California, such field collection is not practical for an area the size of the Sierra Nevada. Consequently, the Forest Service began to investigate remote-sensing technologies at a June 1998 workshop organized by ecologist Carolyn Hunsaker of the Forest Service's Pacific Southwest Research Station in Fresno, Calif. Lidar was identified as one of the promising technologies. The Forest Service is currently designing a new monitoring plan for the Sierra Nevada Framework Project and is actively investigating lidar mapping. The Forest Service will aid the University of Maryland VCL team in processing the new Sierra Nevada data by supplying new ground data from the areas mapped from the air. Once the LVIS maps are publicly available, Forest Service scientists plan to evaluate how well the maps meet their forest management needs for monitoring large forest areas. next: Lidar Lasers: A Safe Technology
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 Vegetation Canopy Lidar Top Left: The Vegetation Canopy Lidar (VCL) mission will map forest canopies, distinguishing between the simple canopy of young forests and the complex, multi-layered structure of old-growth forests. (Photograph courtesy of the University of Maryland) |
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Lidar Lasers: A Safe Technology
During its mapping flights, the LVIS laser is fired 300 times a second as it quickly scans across the flight path of the aircraft. The tiny beam is about the size of a laser pointer beam when it leaves the aircraft and is safe to touch. (If you stood next to the plane and placed your hand in the path of the laser beam, you would not feel any heat.) By the time the laser beam reaches the ground it has spread out to more than 75 feet across. Like a laser pointer, the LVIS laser beam is unsafe to look into directly from close up. But, following the ANSI standards, the LVIS laser is safe to the eye when seen from a distance of half a mile. LVIS will be turned on during its mapping flights only when the plane is more than 4 miles above the ground. Because of the way the laser beam spreads out, it will be about 50 times safer at the ground than required by ANSI standards. An observer on the ground looking up at the plane when the laser is fired would not see any flash of light. back: Applications to Forest Management Needs return to: Earth Observatory Library |
 Vegetation Canopy Lidar |
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The NASA/University of Maryland Vegetation Canopy Lidar
(VCL)
mission will create the first maps of the three-dimensional structure of
vegetation in the world's forests. VCL is scheduled for launch in
September 2000. The mission is the first selected program of NASA's
Earth System Science Pathfinder project.
Over its two-year lifespan, VCL will sample the vast majority of the
Earth's closed canopy forests, from 65 degrees North latitude to 65
degrees South latitude. The spacecraft will be launched into a
260-mile-high orbit from Alaska's new Kodiak Launch Complex. The
University of Maryland Geography Department will house VCL
command-and-control and data processing operations.
An imaging lidar is
the only instrument that can "see" both the finescale vertical and horizontal
structure of a forest. The unique design of LVIS also allows it to readily map
large expanses of forest. LVIS maps should be able to identify specific ages of
forests, such as mature, "old-growth" forests and other habitats associated with
sensitive wildlife species, thus aiding in management decisions about future
uses of these forests.